Nitro-Explosives: A Practical Treatise Part 22

~Ballist.i.te.~--In the case of ballist.i.te the treatment is the same, except that when it is in a very finely granulated condition it need not be cut up.

~Guttmann's Heat Test.~--This test was proposed by Mr Oscar Guttmann in a paper read before the Society of Chemical Industry (vol. xvi., 1897), in the place of the pota.s.sium iodide starch paper used in the Abel test. The filter paper used is wetted with a solution of diphenylamine[A] in sulphuric acid. The solution is prepared as follows:--Take 0.100 grm. of diphenylamine crystals, put them in a wide-necked flask with a ground stopper, add 50 c.c. of dilute sulphuric acid (10 c.c. of concentrated sulphuric acid to 40 c.c. of water), and put the flask in a water bath at between 50 and 55 C. At this temperature the diphenylamine will melt, and at once dissolve in the sulphuric acid, when the flask should be taken out, well shaken, and allowed to cool. After cooling, add 50 c.c. of Price's double distilled glycerine, shake well, and keep the solution in a dark place. The test has to be applied in the following way:--The explosives that have to be tested are finely subdivided, gun-cotton, nitro-glycerine, dynamite, blasting gelatine, &c., in the same way as at present directed by the Home Office regulations. Smokeless powders are all to be ground in a bell-shaped coffee mill as finely as possible, and sifted as. .h.i.therto. 1.5 grm. of the explosive (from the second sieve in the case of smokeless powder) is to be weighed off and put into a test tube as. .h.i.therto used. Strips of well-washed filter paper, 25 mm. wide, are to be hung on a hooked gla.s.s rod as usual. A drop of the diphenylamine solution is taken up by means of a clean gla.s.s rod, and the upper corners of the filter paper are touched with it, so that when the two drops run together about a quarter of the filter paper is moist. This is then put into the test tube, and this again into the water bath, which has been heated to 70 C. The heat test reaction should not show in a shorter time than fifteen minutes. It will begin by the moist part of the paper acquiring a greenish yellow colour, and from this moment the paper should be carefully watched. After one or two minutes a dark blue mark will suddenly appear on the dividing line between the wet and dry part of the filter paper, and this is the point that should be taken.

[Footnote A: Dr G. Spica (_Rivista_, Aug. 1897) proposes to use hydrochloride of meta-phenylenediamine.]

~Exudation and Liquefaction Test for Blasting Gelatine, Gelatine Dynamite, &c.~--A cylinder of blasting gelatine, &c., is to be cut from the cartridge to be tested, the length of the cylinder to be equal to its diameter, and the ends being cut flat. The cylinder is to be placed on end on a flat surface without any wrapper, and secured by a pin pa.s.sing vertically through its centre. In this condition the cylinder is to be exposed for 144 consecutive hours (six days and nights) to a temperature ranging from 85 to 90 F. (inclusive), and during such exposure the cylinder shall not diminish in height by more than one-fourth of its original height, and the upper cut surface shall retain its flatness and the sharpness of its edge.

~Exudation Test.~--There shall be no separation from the general ma.s.s of the blasting gelatine or gelatine dynamite of a substance of less consistency than the bulk of the remaining portion of the material under any conditions of storage, transport, or use, or when the material is subjected three times in succession to alternate freezing and thawing, or when subjected to the liquefaction test before described.

~Picric Acid.~--The material shall contain not more than 0.3 part of mineral or non-combustible matter in 100 parts by weight of the material dried at 160 F. It should not contain more than a minute trace of lead.

One hundred parts of the dry material shall not contain more than 0.3 part of total (free and combined) sulphuric acid, of which not more than 0.1 part shall be free sulphuric acid. Its melting point should be between 248 and 253 F.

~Ammonite, Bellite, Roburite, and Explosives of similar Composition.~-- These are required to stand the same heat test as compressed nitro-cellulose, gun-cotton, &c.

~Chlorate Mixtures.~--The material must not be too sensitive, and must show no tendency to increase in sensitiveness in keeping. It must contain nothing liable to reduce the chlorate. Chlorides calculated as pota.s.sium chloride must not exceed 0.25 per cent. The material must contain no free acid, or substance liable to produce free acid. Explosives of this cla.s.s containing nitro-compounds will be subject to the heat test.

~Page's Regulator.~--The most convenient gas regulator to use in connection with the heat-test apparatus is the one invented by Prof.

F.J.M. Page, B.Sc.[A] (Fig. 49). It is not affected by variations of the barometric pressure, and is simple and easy to fit up. It consists of a thermometer with an elongated gla.s.s bulb 5/8 inch diameter and 3 inches long. The stem of the thermometer is 5 inches long and 1/8 inch to 3/16 inch internal diameter. One and a half inch from the top of the stem is fused in at right angles a piece of gla.s.s tube, 1 inch long, of the same diameter as the stem, so as to form a T. A piece of gla.s.s tube (A), about 7/16 inch external diameter and 1-1/2 inch long, is fitted at one end with a short, sound cork (C, Fig. 50). Through the centre of this cork a hole is bored, so that the stem of the thermometer just fits into it. The other end of this gla.s.s tube is closed by a tightly fitting cork, preferably of indiarubber (I), which is pierced by a fine bradawl through the centre.

Into the hole thus made is forced a piece of fine gla.s.s tube (B) 3 inches long, and small enough to fit loosely inside the stem of the thermometer.

[Footnote A: _Chemical Soc. Jour._, 1876, i. 24.]

The thermometer is filled by pouring in mercury through a small funnel until the level of the mercury (when the thermometer is at the desired temperature) is about 1-1/2 inch below the T. The piece of gla.s.s tube A, closed at its upper extremity by the cork I, through which the fine gla.s.s tube B pa.s.ses into the stem of the thermometer, is now filled by means of the perforated cork at its lower extremity on the stem of the thermometer.

The gas supply tube is attached to the top of the tube A, the burner to the T, so that the gas pa.s.ses in at the top, down the fine tube B, rises in the s.p.a.ce between B and the inside wall of the stem of the thermometer, and escapes by the T. The regulator is set for any given temperature by pushing the cork C, and consequently the tubes A and B, which are firmly attached to it, up or down the stem of the thermometer, until the regulator just cuts off the gas at the desired temperature.

[Ill.u.s.tration: FIG. 49.--PAGE'S REGULATOR.]

[Ill.u.s.tration: FIG. 50.--PAGE'S GAS REGULATOR, SHOWING BYE-Pa.s.s AND CUT-OFF ARRANGEMENT.]

As soon as the temperature falls, the mercury contracts, and thus opens the end of the tube B. The gas is thus turned on, and the temperature rises until the regulator again cuts off the gas. In order to prevent the possible extinction of the flame by the regulator, the bra.s.s tube which carries the gas to the regulator is connected with the tube which brings the gas from the regulator to the burner by a small bra.s.s tap (Fig. 2).

This tap forms an adjustable bye-pa.s.s, and thus a small flame can be kept burning, even though the regulator be completely shut off. It is obvious that the quant.i.ty of gas supplied through the bye-pa.s.s must always be less than that required to maintain the desired temperature. This regulator, placed in a beaker of water on a tripod, will maintain the temperature of the water during four or five hours within 0.2 C., and an air bath during six weeks within 0.5 C.

To sum up briefly the method of using the regulator:--Being filled with mercury to about 12 inch below the T, attach the gas supply as in diagram (Fig. 2), the bra.s.s tap being open, and the tube B unclosed by the mercury. Allow the gas to completely expel the air in the apparatus. Push down the tube A so that the end of B is well under the surface of the mercury. Turn off the tap of the bye-pa.s.s until the smallest bead of flame is visible. Raise A and B, and allow the temperature to rise until the desired point is attained. Then push the tubes A and B slowly down until the flame is just shut off. The regulator will then keep the temperature at that point.

~Will's Test for Nitro-Cellulose.~--The principle of Dr W. Will's test[A]

may be briefly described as follows:--The regularity with which nitro- cellulose decomposes under conditions admitting of the removal of the products of decomposition immediately following their formation is a measure of its stability. As decomposing agent a sufficiently high temperature (135 C.) is employed, the explosive being kept in a constantly changing atmosphere of carbon dioxide, heated to the same temperature: the oxides of nitrogen which result are swept over red-hot copper, and are then reduced to nitrogen, and finally, the rates of evolution of nitrogen are measured and compared. Dr Will considers that the best definition and test of a stable nitro-cellulose is that it should give off at a high temperature equal quant.i.ties of nitrogen in equal times. For the purposes of manufacture, it is specially important that the material should be purified to its limit, i.e., the point at which further washing produces no further change in its speed of decomposition measured in the manner described.

[Footnote A: W. Will, _Mitt. a. d. Centrallstelle f. Wissench. Techn.

Untersuchungen Nuo-Babelsberg Berlin_, 1902 [2], 5-24.]

The sample of gun-cotton (2.5 grms.) is packed into the decomposition tube 15 mm. wide and 10 cm. high, and heated by an oil bath to a constant temperature, the oxides so produced are forced over ignited copper, where they are reduced, and the nitrogen retained in the measuring tubes. Care must be taken that the acid decomposition products do not condense in any portion of the apparatus. The air in the whole apparatus is first displaced by a stream of carbon dioxide issuing from a carbon dioxide generator, or gas-holder, and pa.s.sing through scrubbers, and this stream of gas is maintained throughout the whole of the experiment, the gas being absorbed at the end of the system by strong solution of caustic potash. To guard against the danger of explosions, which occasionally occur, the decomposition tube and oil bath are surrounded by a large casing with walls composed of iron plate and strong gla.s.s.

Dr Will's apparatus has been modified by Dr Robertson,[A] of the Royal Gunpowder Factory, Waltham Abbey. The form of the apparatus used by him is shown in Fig. 51.

~CO_{2} Holders.~--Although objection has been taken to the use of compressed CO_{2} in steel cylinders on account of the alleged large and variable amount of air present, it has, nevertheless, been found possible to obtain this gas with as little as 0.02 per cent. of air. Frequent estimations of the air present in the CO_{2} of a cylinder show that even with the commercial article, after the bulk of the CO_{2} has been removed, the residual gas contains only a very small amount of air, which decreases in a gradual and perfectly regular manner. For example, one cylinder which gave 0.03 per cent. of air by volume, after three months'

constant use gave 0.02 per cent. The advantage of using CO_{2} from this source is obvious when compared with the difficulty of evolving a stream of gas of constant composition from a Kipps or Finkener apparatus. A micrometer screw, in addition to the main valve of the CO_{2} cylinder, is useful for governing the rate of flow. A blank experiment should be made to ascertain the amount of air in the CO_{2} and the correction made in the readings afterwards.

[Footnote A: _Jour. Soc. Chem. Ind._, June 30, 1902, p. 819.]

[Ill.u.s.tration: Fig 51.--Will's Apparatus for Testing Nitro-cellulose]

~Measurement of Pressure and Rate of Flow.~--Great attention is paid to the measurement of the rate of flow of gas, which is arrived at by counting with a stop-watch the number of bubbles of gas per minute in a small sulphuric acid wash bottle. A mercury manometer is introduced here, and is useful for detecting a leak in the apparatus. The rate of flow that gives the most satisfactory results is 1,000 c.c. per hour. If too rapid it does not become sufficiently preheated in the gla.s.s spiral, and if too slow there is a more rapid decomposition of the nitro-cellulose by the oxides of nitrogen which are not removed.

~Decomposition Tube.~--This is of the form and dimensions given by Dr Will (15 mm. wide and 10 cm. high), the preheating worm being of the thinnest hydrometer stem tubing. The ground-in exit tube is kept in position by a small screw clamp with trunnion bearings.

~Bath.~--To permit of two experiments being carried on simultaneously, the bath is adapted for two decomposition tubes, and is on the principle of Lothar Meyer's air bath, that is, the bath proper filled with a high- flashing hydrocarbon oil, and fitted with a lid perforated with two circular holes for the spiral tubes, is surrounded by an asbestos-covered envelope, in the interior of which circulate the products of combustion of numerous small gas jets. The stirrer, agitated by a water motor, or, better still, a hot-air engine, has a series of helical blades curved to give a thorough mixing to the oil. Great uniformity and constancy of temperature are thus obtained. The bath is fitted also with a temperature regulator and thermometer.

~Reduction Tube~--This is of copper, and consists of two parts, the outer tube and an inner reaching to nearly the bottom of the former. Into the inner tube fits a spiral of reduced copper gauze, and into the annular s.p.a.ce between the tubes is fitted a tightly packed reduced copper spiral.

At the bottom the inlet tube dips into a layer of copper oxide asbestos, on the top of which is a layer of reduced copper asbestos. Through the indiarubber cork pa.s.ses a gla.s.s tube, which leads the CO_{2} and nitrogen out of the reduction tube. As the portion of the tube containing the spirals is heated to redness, water jackets are provided on both inner and outer tubes to protect the indiarubber cork.

~Nitrogen Measuring Apparatus.~--The measuring tube with zigzag arrangement is used, having been found very economical in potash. It is most convenient to take readings by counterbalancing the column of potash solution and reading off the volume of gas at atmospheric pressure. For this purpose the tap immediately in front of the measuring tube is momentarily closed, this having been proved to be without ill effect on the progress of the test. In all experiments done by this test the air correction is subtracted from each reading, and the remainder brought to milligrams of nitrogen with the usual corrections. As objection has frequently been taken to the test on the ground of difficulty in interpreting the results obtained, Dr Robertson made a series of experiments for the purpose of standardising the test, and at the same time of arriving at the condition under which it could be applied in the most sensitive and efficient manner. A variety of nitro-celluloses having been tested, there were chosen as typical, of stable and unstable products, service gun-cotton on the one hand, and an experimental gun- cotton, Z, on the other. The first point brought out by these experiments was the striking uniformity of service gun-cotton, first in regard to the rectilinear nature of the curve of evolution of nitrogen, and secondly in regard to the small range within which a large number of results is included, 15 samples lying between 6.6 and 8.7 mgms. of nitrogen evolved in four hours. In the case of service gun-cotton, little difference in the rate of evolution of nitrogen evolved is obtained on altering the rate of pa.s.sage of CO_{2} gas through the wide range of 500 c.c. per hour to 2,500 c.c. per hour. With Z gun-cotton (see Fig. 52), however, the case is very different. Operating at a rate of 1,000 c.c. of CO_{2} per hour, a curve of nitrogen evolution is obtained, which is bent and forms a good representation of the inherent instability of the material as proved to exist from other considerations. Operating at the rate of 1,500 c.c. per hour, as recommended by Dr Will, the evolution of nitrogen is represented by a straight line, steeper, however, than that of service gun-cotton. The rate of pa.s.sage of CO_{2} was therefore chosen at 1,000 c.c. per hour, or two-thirds of the rate of Dr Will, and this rate, besides possessing the advantage claimed of rendering diagnostic the manner of nitrogen evolution in Z gun-cotton, has in other cases been useful in bringing out relationships, which the higher rate would have entirely masked.

[Ill.u.s.tration: Fig. 52.--Dr. Robertson's results.]

[Ill.u.s.tration: Fig. 53.--Service Guncotton for Cordite made at a Private Factory.]

Readings are taken thirty minutes from the time the nitro-cellulose is heated, and are taken at intervals of fifteen minutes for about four hours; fresh caustic potash is added every thirty minutes or so. It is convenient to plot the results in curves. The curves given in Fig. 53 are from gun-cotton manufacturers in England at a private factory. The rate of evolution of nitrogen is as follows:--

In 1 hour. In 2 hours. In 3 hours. In 4 hours.

N. N. N. N. in milligrammes.

1.25 2.55 4.5 5.75 1.5 3.25 5.25 6.75 These results are very satisfactory, the gun-cotton was of a very good quality. Several hours are necessary to remove all the air from the apparatus. Dr Will stated fifteen minutes in his original paper, but this has not been found sufficient. It has not been satisfactorily proved that Will's test can be applied to gelatinised nitro-cellulose powders. It is convenient to plot the results in curves; the nitrogen is generally given in cubic centimetres or in milligrammes, and readings taken every fifteen minutes. The steepness of the curve is a measure of the stability of the nitro-cellulose which is being examined. The steeper the curve the more nitrogen is evolved per unit of time, and the less stable the nitro- cellulose. In the case of unstable nitro-celluloses heated under the conditions described, the separation of nitrogen is much greater at first than at a later period. If the nitro-cellulose be very unstable, explosions are produced. If the separation of nitrogen is uniform during the prolonged heating, then the nitro-cellulose may be regarded as "normal." If it be desired to determine the absolute amount of nitrogen separated from a nitro-cellulose, the following conditions must be observed:--(1.) Accurate weighing of the nitro-cellulose; (2.) Determination of the amount of air in the CO_{2}, and deduction of this from the volume of gas obtained; (3.) Reduction of the volume of the gas to the volume at 0 C. and 760 mm. pressure.[A]

[Footnote A: See also _Jour. Soc. Chem. Ind._, Dec. 1902, pages 1545-1555, on the "Stability of Nitro-cellulose" and "Examination of Nitro- cellulose," Dr Will.]

~Bergrnann and Junk~[A] describe a test for nitro-cellulose that has been in use in the Prussian testing station for some years. The apparatus consists of a closed copper bath provided with a condenser and 10 countersunk tubes of 20 cm. length. By boiling amyl-alcohol in the bath, the tubes can be kept at a constant temperature of 132 C. The explosive to be tested is placed in a gla.s.s tube 35 cm. long and 2 cm. wide, having a ground neck into which an absorption bulb is fitted. The whole apparatus is surrounded by a shield, in case of explosion. In carrying out the test, 2 grms. of the explosive are placed in the gla.s.s tube and well pressed down. The absorption bulb is half filled with water, and fitted into the ground neck of the gla.s.s tube, which is then placed in one of the tubes in the bath previously brought to the boiling point (132 C.). The evolved oxides of nitrogen are absorbed in the water in the bulb, and at the end of two hours the tubes are removed from the bath, and on cooling, the water from the bulb flows back and wets the explosive. The contents of the tube are filtered and washed, the filtrate is oxidised with permanganate, and the nitrogen determined as nitric oxide by the Schultze-Tieman method.

The authors conclude that a stable gun-cotton does not evolve more than 2.5 c.c. of nitric oxide per grm. on being heated to 132 C. for two hours, and a stable collodion-cotton not more than 2 c.c. under the same conditions. The percentage of moisture in the sample to be tested should be kept as low as possible. A sample of nitro-cellulose containing 1.97% of moisture gave an evolution of 2.6 c.c. per grm., while the same sample with 3.4% moisture gave an evolution of over 50 c.c. per grm. Sodium carbonate added to an unstable nitro-cellulose diminishes the rate of decomposition, but if sodium carbonate be intimately mixed with a stable nitro-cellulose the rate of decomposition will be increased. Calcium carbonate and mercury chloride have no influence. If an unstable nitro- cellulose be extracted with alcohol a stable compound is produced. The percentage solubility of a nitro-cellulose in ether-alcohol rises on heating to 132 C. A sample which before heating had a solubility of 4.7% had its solubility increased to 82.5% after six hours' heating.

[Footnote A: _Jour. Soc. Chem. Ind._, xxiii., Oct. 15, 1904, p. 953.]

Mr A.P. Sy (_Jour. Amer. Chem. Soc._, 1903) describes a new stability test for nitro-cellulose which he terms "The Elastic Limit of Powder Resistance to Heat." The test consists in heating the powder on a watch gla.s.s in an oven to a temperature of 115 C., after eight hours the watch gla.s.s and powder are weighed and the process repeated daily for six days or less. He claims that the powder is tested in its natural state, all the products of decomposition are taken into account, whilst in the old tests only the acid products are shown, and in the Will test only nitrogen, that it affords an indication of the effect of small quant.i.ties of added substances or foreign matters on the stability and that it is simple, and not subject to the variations of the old tests.

Obermuller (_Jour. Soc. Chem. Ind._, April 15, 1905) considers Bergmann and Junk's test is too complicated and occupies too much time; he proposes to heat gun-cotton to 140 C. _in vacuo_, and to measure continuously by means of a mercury manometer the pressure exerted by the evolved gases, the latter being maintained at constant volume; the rate at which the pressure increases is a measure of the rate of decomposition of the nitro- cellulose.

SPECIFIC GRAVITIES OF EXPLOSIVES, &C.

Nitro-glycerine 1.6 Gun-cotton (dry) 1.06 " (25 per cent. water) 1.32 Dynamite No. 1 1.62 Blasting gelatine 1.54 Gelatine dynamite 1.55 Ballist.i.te 1.6 Forcite 1.51 Tonite 1.28 Roburite 1.40 Bellite 1.2-1.4 Carbo-dynamite 1.5 Turpin's cast picric acid 1.6 Nitro-mannite 1.6 Nitro-starch 1.5 Emmensite 1.8 Mono-nitro-benzene 1.2 Meta-di-nitro-benzene 1.575 at 18 C.

Ortho-di-nitro-benzene 1.590 "

Para-di-nitro-benzene 1.625 "

British gunpowder, E.X.E. 1.80 " " S.B.C. 1.85 Cannonite (powder) 1.60 Celluloid 1.35 Cellulose 1.45 Ammonium nitrate 1.707 Mercury fulminate 4.42

TABLE OF THE TEMPERATURE OF DETONATION.

Blasting gelatine 3220 Nitro-glycerine 3170 Dynamite 2940 Gun-cotton 2650 Tonite 2648 Picric acid 2620 Roburite 2100 Ammonia nitrate 1130

RELATIVE SENSITIVENESS TO DETONATION (by Professor C.E. Munroe, U.S. Naval Torpedo Station).

__________________________________________________________________________ | | Maximum | | Distance | | at which | | Detonation | | occurred. | | CM. | | | Gun-cotton | 10 | Nitro-glycerine 86.5 nitro-cotton | | 9.5, camphor 4 per cent.

Explosive gelatine | 20 | NH_{4}NO_{3} 5 parts, (camphorated) | | C_{6}H_{4}(N0_{3})_{2} 1 part.